Hawkweeds
(Hieracium spp.)
TIPS
Updated July 2014
About Hawkweeds
Distribution in BC
(IAPP Aug. 2013)
There are 14 species of native
hawkweeds in western North
America, of which 8 have
been recorded in BC. There
are also 14 species of invasive,
non-native hawkweeds in
western North America, of
which 13 have been recorded
in BC. Twelve of the 13 invasive
species have yellow flowers.
Hawkweeds are readily hybridizing in BC, which can make
identification very difficult. Most invasive hawkweed species
have similar biology, ecological characteristics, impacts,
distributions, and recommended management techniques;
as a result, they are discussed as a complex in this document.
Where necessary for identification purposes, the complex is
divided into either ‘orange’ or ‘yellow’ invasive hawkweeds.
Legal Status
Orange hawkweed is currently the only invasive hawkweed
species regulated by the Weed Control Act. Both meadow
and orange hawkweed are identified in the Forest and
Range Practices Act.
Distribution
Invasive hawkweeds are currently distributed throughout
most forest regions and regional districts in BC. The regional
districts east of the Rocky Mountains, Northern Rockies, and
Peace River Regional Districts only have a few known
invasive hawkweed sites and efforts to prevent further
establishment and spread are actively underway. Orange
hawkweed is regionally noxious in the East Kootenay,
Central Kootenay, Columbia-Shuswap, Thompson-Nicola,
Bulkley Nechako, and Cariboo Regional Districts.
L. Wilson
L. Wilson
Leaves: Found at base of stem in
rosette formation. Orange: 4-20cm
long; hairy on both upper and lower
surfaces. Yellow: no leaves or greatly
reduced stem leaves, whereas
native yellow species have true
leaves all the way up their stems;
some species have glaborous leaves
(no hairs).
Fruits: Dark ribbed achenes; tiny,
approximately 2 mm long.
Similar Species: Further information
on hawkweed identification:
www.for.gov.bc.ca/hra/Publications/
invasive_plants/Hawkweed_key_PNW_2007.pdf
© The Illustrated
Flora of BC
Ecological Characteristics
Habitat: Flourishes in well-drained, coarse-textured soils. Can
invade natural open areas and disturbed sites, including
roadsides, pastures, and clearings.
Identification
Flowers: Bright orange, orange-red, or yellow ray flowers
with several flower heads in clusters atop each stem.
Stems: Orange hawkweed stems are usually single and
un-branched; leafless; contain a milky fluid; covered in
black hairs; 0.3-1.2 m tall. Yellow hawkweed stems, like
orange hawkweed, have short, stiff hairs with the upper
portion of the stem often black and gland tipped.
Reproduction: Perennial species that reproduces through four
mechanisms: (i) above-ground runners (called stolons), (ii)
rhizomes, (iii) seed, and in some cases (iv) buds on the roots.
Established populations expand in size primarily via stolons.
Dispersal: Spreads by intentional and accidental human
activities, wind, animals, and in contaminated hay and soil.
TOGETHER • PREVENT • RESTORE
Impacts
Economic: Forms dense mats of rosettes; out-competes
forage plants in hay fields and pastures. Main impact on
forest industry is the risk of establishment and spread along
roads or areas that are not reforested.
Ecological: Invasive hawkweed species can replace native
vegetation in open, undisturbed natural areas, such as
meadows, and in disturbed areas, such as roadsides, thereby reducing forage and threatening biodiversity.
B. Stewart
Integrated Pest Management
IPM is a decision-making process that includes identification and
inventory of invasive plant populations, assessment of the risks that
they pose, development of well-informed control options that may
include a number of methods, site treatment, and monitoring.
Prevention
• Fertilizer and soil fertility management.
• Minimize soil disturbance and promptly re-vegetate disturbed areas.
• Do not purchase wildflower seed mixes that contain invasive hawkweed species.
Mechanical Control
• Dig out rosettes and their shallow roots in new, small
infestations.
• Take care not to spread any of the vegetative parts of the plant as re-growth from roots, stolons and
rhizomes can occur.
• Although mowing removes flower stems and may
prevent seed set, it should be used with caution as it encourages enhanced vegetative spread.
Biocontrol
• Currently no biocontrol agents are available for orange hawkweed; however, research is underway.
Chemical Control
Herbicide recommendations and use must consider site
characteristics and be prescribed based on site goals and
objectives. Herbicide labels and other sources of
information must be reviewed before selecting and
applying herbicides.
Thank you to the BC Ministry of Environment for
providing project funding, and to those who
advised the development of these management
recommendations.
B. Stewart
B. Stewart
L. Scott
• Application of pesticides on Crown land must be
carried out following a confirmed Pest Management
Plan (Integrated Pest Management Act) and under the
supervision of a certified pesticide applicator.
www.env.gov.bc.ca/epd/ipmp/
References/Links
• Antos, J., et al. 1996. Plants of southern interior British
Columbia. Lone Pine Publishing, Vancouver, BC.
• BC Ministry of Agriculture. 2001.
www.agf.gov.bc.ca/cropprot/ipm.htm
•
BC Ministry of Forests, Lands, and Natural Resource Operations,
Invasive Alien Plant Program (IAPP).
www.for.gov.bc.ca/hra/Plants/application.htm
• Callihan, R.H., Wilson, L.M., McCaffrey, J.P., and Miller,
T.W. 1997. Hawkweeds. A Pacific Northwest Extension Publication 499. www.weedsbc.ca/pdf/orange_hawkweed.pdf
•
E-Flora BC, an Electronic Atlas of the Plants of BC.
www.eflora.bc.ca/
• Field Guide to Noxious and Other Selected Weeds of British Columbia. 2002. http://www.agf.gov.bc.ca/cropprot/
weedguid/orangehw.htm
• University of Idaho Hawkweed Website. www.cals.uidaho.edu/hawkweed/
ADDITIONAL CONTACT INFO
• In soils with low nitrogen and sulphur levels (such as pastures and range areas), where grass species are growing amongst the hawkweed, the competitive ability of grasses can be increased through
application of fertilizer with nitrogen and sulphur
components.
• Spring treatments with both nitrogen fertilizer and
herbicide are recommended; however, fall herbicide treatments are also effective for control.
• Actively growing plants can be effectively controlled with clopyralid, picloram, picloram plus 2,4-D,
aminopyralid, or aminopyralid plus 2,4-D.
• Clopyralid and glyphosate give short term control to suppression of orange hawkweed.
L. Wilson
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